This invention relates to the presulfurization of catalysts.
It will be recalled briefly that often the sulfurizing agent used by refiners is, in prior art, either hydrogen sulfide that is pure or diluted with hydrogen or gaseous hydrocarbons, or also dimethyl disulfide diluted with hydrogen, or other sulfur compounds such as alkyl sulfides or alkyl mercaptans, diluted with hydrogen (see U.S. Pat. No. 4,172,027).
The metals of catalysts used in refining, hydrorefining or in petrochemistry, whether they be new or regenerated, are most often in oxidized form, at times in metal form (for some metals of reforming catalysts in particular). The metals of these catalysts, often being active only in sulfurized or at least partially sulfurized form, it is necessary therefore for the refiner or the petrochemist to perform a sulfurizing of the catalyst prior to its use.
As explained above, regeneration of the catalysts is increasingly performed by a specialist in the regeneration of catalysts, at times far from the industrial unit. It seems reasonable to think of restoring to the refiner a product ready for use, which was made possible by the efficient processes of the applicant of U.S. Pat. Nos. 4,530,917, 4,719,195 or EP-B-181,254) in which a sulfur compound is incorporated in the catalytic compound, said compound, causes the sulfurizing or the presulfurizing of the catalyst when, subsequently, in the reaction zone (zone for treating the charge) or in the immediate proximity of the reaction zone, the catalyst will be put into contact, for example, with hydrogen.
More precisely, in European patent EP-B-181,254, the sulfurizing process of the catalyst is characterized by a preliminary stage of incorporation in the catalytic compound of a sulfur compound, of a specific nature.
The preliminary stage of introduction of a sulfur compound, that arbitrarily is called "off-site" or "ex situ," whether it be performed close to the site of the industrial unit or at a more or less geographically great distance from the industrial unit (where the catalyst has been regenerated or where it has been manufactured, for example) is in any case no longer done in the immediate vicinity of the reactor (arbitrarily written "in situ"), i.e. at the head of the reactors or in the zones more or less directly connected with these reactors, necessitating operation under operating conditions (temperature, pressure or others), imposed at least in part by the operating conditions of the reactors themselves or the accessory zone of these reactors (preliminary hydrogenation zone of the catalyst, for example).
The process of EP-B-181,254 makes it possible, to intiate, when the catalyst is subjected from its start preferably on site ("in situ"), to the standard activation reaction in the presence of hydrogen (generally above 100.degree. C.) to initiate, as a result of the presence of hydrogen on the site, sulfurizing at the rate required either, stoichiometric or non-stoichiometric, one or more active metals entering the composition of the catalyst. The process involves incorporating in a first stage, in the absence of hydrogen, in the porosity of the new or regenerated catalyst at least one sulfurizing agent, the sulfurizing agent being a polysulfide of the general formula: EQU R--S.sub.(n) --R'.
Said sulfurizing agent is used in solution in a solvent.
In the second stage, performed "in situ," and preferably above 150.degree. C., an activation stage of the catalyst performed in the presence of hydrogen is initiated, the amount of sulfur required being fixed, thanks to the presence of hydrogen, on the metal or metals entering the composition of said catalyst.
In the polysulfide of the formula: EQU R--S.sub.(n) --R'
n is an integer from 3 to 20, preferably from 4 to 8 and more particularly from 5 to 7; R and R', identical or different, represent organic radicals each containing 1 to 150 carbon atoms per molecule, preferably either 10 to 60 carbon atoms or 5 to 40 carbon atoms and more particularly 7 to 16, these radicals being chosen from the group consisting of alkyl radicals, i.e. saturated or unsaturated, linear or branched or of naphthenic type, aryl radicals, alkylaryl radicals and arylalkyl radicals, these various radicals may also contain at least one heteroatom. R' optionally also can be a hydrogen atom.
As a preferred example of polysulfide, the ditertiododecyl polysulfide (n=5) where R and R' are each a dodecyl radical can be cited.
This product is marketed for example by ELF AQUITAINE under the name TPS 32, particularly because it contains about 32% by weight of sulfur.
Ditertiononyl polysulfide (n=5) where R and R' are each a tertiononyl radical also can be cited.
This product is marketed by ELF AQUITAINE under the name TPS 37, particularly because it contains about 37% by weight of sulfur or by PENNWALT under the name TNPS.
For reasons of procedure, these sulfurizing agents of polysulfide type obviously can be used alone or as a mixture, in proportions chosen judiciously.
The first stage mentioned above is performed in the absence of hydrogen and makes it possible to obtain with very great precision the degree of total or partial sulfurizing requested by the user. This incorporation of sulfur is performed between 0.degree. and 50.degree. C. and preferably between 10.degree. and 35.degree. C. and preferably still at ambient temperature.
The sulfurizing agent is used, diluted in a suitable solvent which depends particularly on the nature of the sulfurizing agent, i.e. on R and R', radicals which determine the content of sulfur incorporated in the catalyst generally by capillary action or by porosity. The sulfurizing processes actually vary according to the cuts to be treated subsequently in the presence of catalysts treated according to the invention.
At the end of this first stage, a second stage is initiated which is divided into two parts:
The first part of this second stage is performed in situ or ex situ. The first part of the second stage is performed in the absence of hydrogen. It is performed in the presence of air or an inert gas. According to a preferred method, it is performed in the presence of at least steam or at least moist air or a moist inert gas during at least about 5 minutes, "in situ" or "ex situ" at a temperature between 65.degree. and 270.degree. C. under a pressure between about 0.5 and 70 bars (0.05 and 7 MPa), the catalyst then being dried.
Subsequently, on site or in the proximity of the site (on which the catalyst will be used for the treatment of various charges), at the time of the standard activation reaction, performed in the presence of hydrogen (second stage of the process of European patent application EP-B-181,254), the sulfurizing agent, introduced in the catalyst in predetermined amounts, will be capable of producing hydrogen sulfide which, in the presence of hydrogen, will lead to the desired sulfide or sulfides of the metal or metals present in the catalyst.
Preferably, the operation can take place for at least 5 minutes and preferably at most 10 hours between 65.degree. and 265.degree. C., under a pressure between 0.5 and 70 bars (0.05 and 7 MPa), preferably between 85.degree. and 260.degree. C. and more particularly between 95.degree. and 150.degree. C.
When working in the presence of steam, the latter should be superheated to at least 110.degree. C.
When operating in the presence of moist inert gas or moist air, it is advisable to operate with a relative humidity on the order of 2 to 60% by volume at the drying stage, and at a temperature between 105.degree. and 200.degree. C., preferably between 110.degree. and 170.degree. C. A gas also can be used whose water content is between 50 and 100% (pure steam), preferably between 90 and 100% and operated between 5 minutes and 10 hours under 0.05 to 7 MPa at a temperature lower than 200.degree. C., preferably lower than 170.degree. C.
During the second stage, the catalyst is brought to a temperature equal to at least 275.degree. C., for at least 1 minute.
The second part of the second stage generally is performed in situ and therfore can merge with the starting or the running itself of the refining and petrochemical reaction for which the catalyst prepared according to this invention is designed, in the case where precisely such a reaction is performed above 275.degree. C.
When the temperature chosen for the refining or petrochemical reaction is lower than 275.degree. C. (for example, this can be the case of hydrodesulfurizing of gasolines or kerosenes), it then is sufficient to lower the temperature used for activation of the catalyst in the second part of the second stage after this stage to the temperature appropriate for the refining or petrochemical reaction.
It has been found that in the first part of the second stage, despite the absence of hydrogen, the catalyst is sulfurized, i.e., the oxides of active metals of the catalyst, are converted into sulfides. This phenomenon is easily observed by analysis of the catalyst, which furthermore becomes black. On the other hand, chemisorption tests show that as long as the catalyst does not reach the temperature of 275.degree. C. and does not remain at least several minutes at at least 275.degree. C., this catalyst remains without catalytic activity.